1. Field of the Disclosure
Embodiments described herein generally relate to a physics-based approach to model and optimize metal-oxide-semiconductor field-effect transistor (MOSFET) devices.
2. Background Art
As process technology continues to reduce dimensions, process variation becomes a major source of yield loss. Circuit simulation and timing analysis tools are needed to correctly account for process variations in order to avoid the inherent pessimism of the traditional methodologies and timing analyses. Statistical timing analysis tools have been recently developed to provide more accurate and powerful timing analysis of digital circuits.
Inherent equipment and environment fluctuations in the semiconductor fabrication process create a variation in device and circuit performance. While every effort is made in the fabrication process, and also in the design process, to reduce the magnitude and the impact of these variations, some level of variation can not be avoided and may become a limiting factor in the performance of the technology.
Traditional approaches of modeling variations have been through the definition of “corner models.” These corner models are usually defined in terms of the ranges for drive currents or threshold voltages. For example, fast-fast and slow-slow corners refer to process points where both p-channel and n-channel devices are at their maximum (or minimum) saturation drive current (“Id-sat”) conditions. In traditional circuit designs, the design may be simulated at the corners and checked for functionality and the conforming to specified characteristics. Similar approaches may be used in static timing analysis. The timing boundaries may be checked at specific process or environmental points. Traditional corner methodologies may also assume that all parameters vary independently over a specified range.
In reality, however, most parameters are correlated and dependent. Due to this limitation, the traditional corner methodologies may not accurately reflect the impact of the variations and may be inherently too pessimistic or too optimistic, depending on the circuit characteristics of interest and the metrics on which the corners exemplify.